Project I's overall goal is to develop evidence-based definitions of 3 specific language disabilities in written language (SLDs-WL): Impaired Handwriting; Impaired Word Reading/Spelling; Impaired Reading Comprehension/WrittenExpression. Research Aim 1 is to test Hypothesis 1 that the prior findings of relationships between unique impairments in Learning Profiles (patterns of impaired and non-impaired reading, writing, and oral language skills) and unique impairments in Phenotype Profiles (working memory storage and processing units, loops, and executive functions for supervisory attention), replicate. Research Aim 2 is to test Hypothesis 2 that each ofthe 3 SLDs-WL will differentially predict response to intervention (RTI) during the portion of the specialized instruction tailored to the nature of the impairment in a specific SLD-WL: slower RTI and less stability on written language outcomes for its defining impairment(s) compared to the other 2 SLDs-WL and controls from pretest to posttest (following specialized instruction) to long-term follow-up 1 (about a year later) and follow-up 2 (about 2 years later). Specific Aim 3 is to test Hypothesis 3 that professional development of teachers will improve language learning and phenotype skills further and/or maintain them if next year's language arts teacher receives professional development on language, executive functions, and differentiated instruction after follow-up 1; to test it, student outcomes between long- term follow-ups 1 and 2 will be compared. Specific Aim 4 is to test Hypothesis 4 that interdisciplinary variables explain RTI better (explain unique variance and more variance) than variables from a single discipline: motivation, brain, gene, working memory phenotype, and language learning measures will be used as predictors in cross-center multiple regressions of longitudinal RTI. To accomplish its research aims. Project I will work closely with Projects II, III, and Administrative Core A and Service Core B. RELEVANCE (See instructions): Students with SLDs-WL are at risk for grade retention, school-drop out, failure to graduate from high school or gain access to higher education, dificulties in some work environments, and mental health problems resulting from their disabilities and lack of school success. The proposed research may lead to evidence- based definitions used for differential diagnosis and instruction to reduce the number of students with these adverse educational and mental health outcomes.